The present invention is directed to actuator valves for air driven reciprocating devices. More specifically, the present invention is directed to an actuator valve for reciprocating devices wherein the valve includes a control rod which reciprocates with the driven mechanism and a pneumatically controlled valve piston.
Actuator valves for reciprocating pneumatically driven devices have been developed which employ a pilot valve or rod responsive to the position of the reciprocating element of the device and a pneumatically controlled valve piston responsive to the pilot rod position. The valve piston in turn controls the incoming flow of pressurized air to provide an alternating flow to the reciprocating element. This alternating flow forces the element to stroke back and forth thereby performing work and driving the pilot rod. Such actuator valves thus convert a relatively steady source of pressurized air into an alternating flow without need for any outside timing or control system. The source air pressure alone drives the valve as well as the working device.
One such actuator valve used primarily on air driven diaphragm pumps is disclosed in U.S. Pat. No. 3,071,118, the disclosure of which is incorporated herein by reference. This pump system has included air driven diaphragms positioned on either side of an actuator valve in an arrangement substantially identical, outwardly of the actuator valve and pilot or control rod, to the pump shown in FIG. 1 herein. In the earlier actuator valves employed with these pumps, the valve piston has been oriented vertically and the pilot rod has included two axial passages for selectively venting the appropriate ends of the chamber within which the valve piston is to operate. Vents for the axial passages have been positioned outwardly of the valve piston vents along the passageway through which the control rod extends. In this way each axial passage on the control rod vents one end of the cylinder within which the valve piston operates through inward movement of one of the axial passages on the control rod until that axial passage becomes exposed to a valve piston vent. To accommodate this operation, the rod and its path of travel through the actuator valve is exposed to the pressurized air of the system. Another control rod and vent arrangement is disclosed in co-pending patent application, Ser. No. 38,685, filed May 14, 1979, now U.S. Pat. No. 4,242,941, the disclosure of which is incorporated herein by reference.
Normally the control for both the actuator valve and the pump it drives is through control of the air supply driving the device. However, when close control of the pump output is required, many users have found that the pump output may be valved and the air pressure to the device left on. As a result, the pump is stalled or approaches a stalled condition as the output is cut back or closed off. Pressurized air remains, in this stalled condition, in the valve piston cylinder and in one of the two pump air chambers.
Heretofore, the actuator valves of the type disclosed in U.S. Pat. No. 3,071,118 would use air which did not perform useful work in either operating the valve or in driving the associated reciprocating device. This air escaped from the actuator valve by the control rod. When the pump was in either the stalled condition or near stalled condition, the loss of air became noticeable and in some applications objectionable. Particular attention has also been directed to this wasting of pressurized air because of the resulting waste of energy. Furthermore, in the stalled condition, the wasted air detracted from the power available to the associated reciprocating device.